1. Field of the Invention
The present invention relates to a disk drive system for a data storage disk and, more particularly, to a mechanism for selectively positioning a read/write arm in the absence of electrical power to the disk drive system.
2. Description of Prior Art
In electronic data handling, systems are well known in which data is stored in binary form on the face of a rotatable disk. In magnetic recording systems, for example, the binary data is encoded upon, or retrieved from, the face of the disk in concentric tracks by a movable electromagnetic transducer which is selectively positioned at positions radial of the disk in order to locate a particular track at which information is to be recorded or retrieved. A typical five and one-quarter inch diameter disk, for example, has four hundred to six hundred tracks for data storage formed upon its face.
Various systems are known to accurately and quickly place such transducers upon a desired track on the face of a disk. Some systems, for example, depend upon positional information which is encoded upon the individual tracks on the face of the disk; and other other systems rely upon a record of past movements of the transducer. In systems of the latter type, difficulties can arise when power is interrupted to the disk drive system thereby causing the control system to lose knowledge of the exact position of the transducer. In such situations, errors may arise when the power to the disk drive system is resumed and an effort is made to reposition the transducer on the face of the disk.